1. Field of the Invention
The present invention relates to an electrochemical process and cell for mercerizing, souring, and bleaching textiles such as cotton fabrics, mixed fabrics, and paper products.
2. Description of Related Art
Mercerization is a textile treatment process that uses caustic solutions to modify the structure of cotton to improve dye affinity and uptake. Mercerization also improves the strength and luster of the fabric. A process similar to mercerization, scouring, uses a lower concentration of caustic (0.5-6.0% vs. .about.22%) to remove dirt, oils, and sizing agents from fabrics. After a fabric is mercerized, the last traces of caustic are removed, first by washing and then by an acid neutralization treatment called souring. Souring treats the mercerized material with an acid to remove residual base.
In addition to mercerization and souring, the cotton fabrics are often bleached by adding oxidants to either the mercerizing or souring bath, or in separate unit processes. Bleaching is used to disinfect and remove color from the mercerized fabric. Typical bleaches include hypochlorite in caustic, hydrogen peroxide, perborates, perphosphates, and sometimes ozone. Bleaching generates large quantities of wash water and requires large purchases of bleaches each year.
Approximately five billion pounds of cotton-based fabrics are mercerized and soured annually in the United States. Large quantities of wash water, caustic, and neutralizing acid are consumed by the textile industry each year. The spent caustic, souring, and washing waters are often recycled by filtering and concentrated by evaporation to reduce waste of these materials.
Because of the high cost, energy consumption, and effluent production in the conventional mercerization process, an improved process for textile treatment is needed that can achieve mercerization, souring, and bleaching at a lower cost, with lower energy demands, and with reduced effluent. Since water can be electrolyzed to produce acids, bases, and hydrogen peroxide bleach, the concept of using electrolysis of neutral solutions to make base for mercerization of fabrics has been investigated.
A Soviet technique employs electrochemical treatment of a cotton fabric in aqueous solution of sodium sulfate using controlled current density between two electrodes. (See Bogdanovskaya, V. A., Krupennikova, S. N., and Zakharov, A. G., "Mercerization and electrochemical sanitation of cotton fabric", Soviet Certificate of Authorship and Soviet Patent SU 1689467, Nov. 7, 1991.) At the cathode, water is reduced to form hydrogen gas and base. At the anode, water is oxidized to produce oxygen gas and acid. Favorable results in the treatment of unmercerized cotton were reported.
A preferred process for mercerization of textiles would not produce hydrogen gas bubbles in the production of caustic compound, thereby avoiding the need to mitigate hazards associated with the evolution of hydrogen gas. In addition, an improved process would bleach the fabric in addition to mercerizing and souring. Reductions in energy requirements, effluent production, and reagent volume are clearly desirable. The present invention satisfies these conditions and can be used to mercerize, sour, and bleach textiles using a monopolar or bipolar electrochemical cell.